1. Field of the Invention
The present invention relates to a system and method for actuation of a valve, such as an intake and/or exhaust valve of an internal combustion engine.
2. Background Art
Electromagnetic or electronic valve actuation (EVA) offers greater control authority and can significantly improve engine performance and fuel economy under various operating conditions relative to conventional camshaft arrangements. EVA systems use electromagnetic actuators to electrically or electronically open and close the intake and/or exhaust valves.
Electromagnetic actuators controlled by an associated valve controller, engine controller, and/or vehicle controller may use electromagnets or solenoids to attract an armature that operates on the valve stem. In a typical electromagnetic actuator, two opposing electromagnets and associated springs are used to open and close an engine valve in response to the signals generated by the controller. The upper and lower electromagnets are energized to assist the springs in closing and opening the valve, respectively, and to hold the valve closed or open against the associated spring force. The upper spring exerts a downward force that pushes the valve downward as the upper electromagnet is turned off, while the lower spring exerts an upward force that pushes the valve upward as the lower electromagnet is turned off. The opening, closing, and landing speeds of the valve are functions of a number of parameters including the spring forces and the excitation currents of the electromagnets.
Prior art EVA control strategies have incorporated one or more capacitors in the control circuitry for energy recovery. For example, Japanese patent application 10-282974 (Pub. No. 2000-110593) published Apr. 18, 2000 discloses the use of capacitors to store energy released during shut off of a coil to power the same coil and/or an alternate or following coil during a subsequent energization. Similarly, U.S. Pat. No. 3,896,346 discloses a parallel or shunting capacitor to store energy recovered from one coil during de-energization to subsequently energize another coil. Japanese patent application 2001-183078 (Pub. No. 2003-007532) published Jan. 10, 2003 discloses the use of a capacitor to recover energy stored in one coil and transfer the energy to a low voltage power supply for subsequent use.
Some prior art EVA control strategies have employed dual “H” bridges to separately control the two electromagnets to control valve movement. This approach typically requires power electronics for each actuator coil. In addition, conventional “H” bridge circuitry regenerates energy and current flows backward through various “H” bridge components to the power supply when reverse voltage is applied to the holding coil during launch, which may result in wasted energy. In addition, such an arrangement requires additional “H” bridge components to allow applied coil voltage to be reversed.
Japanese patent application 2001-183078 (Pub. No. 2003-007532) published Jan. 10, 2003 (described above) discloses actuators having permanent magnets used in combination with electromagnets to provide an attractive force to move/hold the valve. The upper and lower electromagnet coils are arranged in series with corresponding “H” bridge drive electronics to generate a current flow that lowers the force of the permanent magnet to launch the armature, while using the same current to generate an attractive force in the second electromagnet to catch the armature (in combination with the attractive force of a second permanent magnet). The current is then reversed to provide a repelling, braking force to land the valve. The reverse current is also used to generate a force relative to the second permanent magnet to again launch the armature, while generating an attractive force by the first electromagnet to catch the armature (in combination with the first permanent magnet force).